Typically, a double container (a so-called delamination container) including a container main body and a check valve has been known (see, e.g., Patent Literatures 1 and 2). The container main body has an outer shell and an inner bag, and the inner bag contracts in association with a decrease in contents. The check valve is configured to adjust air outflow/inflow between an external space of the container main body and an intermediate space formed between the outer shell and the inner bag.
In the delamination container disclosed in Patent Literature 1, a valve is built in a cap attached to a port portion of the container main body. In the delamination container disclosed in Patent Literature 2, a valve is provided on the inside of a body portion of the outer shell.